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Flatten nested JSON to array of unique objects without indexes

benny
January 25, 2023
220 views
2 votes
3 Answers

I have this simple nested object which I need to flatten to be able to insert it into my database.

const input = {
  name: "Benny",
  department: {
    section: "Technical",
    branch: {
      timezone: "UTC",
    },
  },
  company: [
    {
      name: "SAP",
      customers: ["Ford-1", "Nestle-1"],
    },
    {
      name: "SAP",
      customers: ["Ford-2", "Nestle-2"],
    },
  ],
};

The desired result is like this, each value in the arrays results in a new sub-object stored in an array:

[
  {
    name: "Benny",
    "department.section": "Technical",
    "department.branch.timezone": "UTC",
    "company.name": "SAP",
    "company.customers": "Ford-1",
  },
  {
    name: "Benny",
    "department.section": "Technical",
    "department.branch.timezone": "UTC",
    "company.name": "SAP",
    "company.customers": "Nestle-1",
  },
  {
    name: "Benny",
    "department.section": "Technical",
    "department.branch.timezone": "UTC",
    "company.name": "SAP",
    "company.customers": "Ford-2",
  },
  {
    name: "Benny",
    "department.section": "Technical",
    "department.branch.timezone": "UTC",
    "company.name": "SAP",
    "company.customers": "Nestle-2",
  },
]

Instead of the result below which all fields stored in single object with indexes:

{
  name: 'Benny',
  'department.section': 'Technical',
  'department.branch.timezone': 'UTC',
  'company.0.name': 'SAP',
  'company.0.customers.0': 'Ford-1',
  'company.0.customers.1': 'Nestle-1',
  'company.1.name': 'SAP',
  'company.1.customers.0': 'Ford-2',
  'company.1.customers.1': 'Nestle-2'
}

My code looks like this:

function flatten(obj) {
  let keys = {};
  for (let i in obj) {
    if (!obj.hasOwnProperty(i)) continue;
    if (typeof obj[i] == "object") {
      let flatObj = flatten(obj[i]);
      for (let j in flatObj) {
        if (!flatObj.hasOwnProperty(j)) continue;
        keys[i + "." + j] = flatObj[j];
      }
    } else {
      keys[i] = obj[i];
    }
  }
  return keys;
}

Thanks in advance!

Answers

Edit

In the code below, I left your flatten functionality the same. I added a fix method that converts your original output into your desired output.

Note: I changed the name value of second company to FOO.

const flatten = (obj) => {
  let keys = {};
  for (let i in obj) {
    if (!obj.hasOwnProperty(i)) continue;
    if (typeof obj[i] == 'object') {
      let flatObj = flatten(obj[i]);
      for (let j in flatObj) {
        if (!flatObj.hasOwnProperty(j)) continue;
        keys[i + '.' + j] = flatObj[j];
      }
    } else {
      keys[i] = obj[i];
    }
  }
  return keys;
};

const parseKey = (key) => [...key.matchAll(/(w+).(d)(?=.?)/g)]
  .map(([match, key, index]) => ({ key, index }));

const fix = (obj) => {
  const results = [];
  Object.keys(obj).forEach((key) => {
    const pairs = parseKey(key);
    if (pairs.length > 1) {
      const result = {};
      Object.keys(obj).forEach((subKey) => {
        const subPairs = parseKey(subKey);
        let replacerKey;
        if (subPairs.length < 1) {
          replacerKey = subKey;
        } else {
          if (
            subPairs.length === 1 &&
            subPairs[0].index === pairs[0].index
          ) {
            replacerKey = subKey
              .replace(`.${subPairs[0].index}`, '');
          }
          if (
            subPairs.length === 2 &&
            subPairs[0].index === pairs[0].index &&
            subPairs[1].index === pairs[1].index
          ) {
             replacerKey = subKey
              .replace(`.${subPairs[0].index}`, '')
              .replace(`.${subPairs[1].index}`, '');
             result[replacerKey] = obj[subKey];
          }
        }
        if (replacerKey) {
          result[replacerKey] = obj[subKey];
        }
      });
      results.push(result);
    }
  });
  return results;
};


const input = {
  name: "Benny",
  department: { section: "Technical", branch: { timezone: "UTC" } },
  company: [
    { name: "SAP", customers: ["Ford-1", "Nestle-1"] },
    { name: "FOO", customers: ["Ford-2", "Nestle-2"] },
  ]
};

const flat = flatten(input);
console.log(JSON.stringify(fix(flat), null, 2));

.as-console-wrapper { top: 0; max-height: 100% !important; }

Original response

The closest (legitimate) I could get to your desired result is:

[
  {
    "name": "Benny",
    "department.section": "Technical",
    "department.branch.timezone": "UTC",
    "company.name": "SAP",
    "company.customers.0": "Ford-1",
    "company.customers.1": "Nestle-1"
  },
  {
    "name": "Benny",
    "department.section": "Technical",
    "department.branch.timezone": "UTC",
    "company.name": "SAP",
    "company.customers.0": "Ford-2",
    "company.customers.1": "Nestle-2"
  }
]

I had to create a wrapper function called flattenBy that handles mapping the data by a particular key e.g. company and passes it down to your flatten function (along with the current index).

const flatten = (obj, key, index) => {
  let keys = {};
  for (let i in obj) {
    if (!obj.hasOwnProperty(i)) continue;
    let ref = i !== key ? obj[i] : obj[i][index];
    if (typeof ref == 'object') {
      let flatObj = flatten(ref, key);
      for (let j in flatObj) {
        if (!flatObj.hasOwnProperty(j)) continue;
        keys[i + '.' + j] = flatObj[j];
      }
    } else { keys[i] = obj[i]; }
  }
  return keys;
}

const flattenBy = (obj, key) =>
  obj[key].map((item, index) => flatten(obj, key, index));


const input = {
  name: "Benny",
  department: { section: "Technical", branch: { timezone: "UTC" } },
  company: [
    { name: "SAP", customers: ["Ford-1", "Nestle-1"] },
    { name: "SAP", customers: ["Ford-2", "Nestle-2"] },
  ]
};

console.log(JSON.stringify(flattenBy(input, 'company'), null, 2));

.as-console-wrapper { top: 0; max-height: 100% !important; }

You could take the array’s values as part of a cartesian product and get finally flat objects.

const
    getArray = v => Array.isArray(v) ? v : [v],
    isObject = v => v && typeof v === 'object',
    getCartesian = object => Object.entries(object).reduce((r, [k, v]) => r.flatMap(s =>
        getArray(v).flatMap(w =>
            (isObject(w) ? getCartesian(w) : [w]).map(x => ({ ...s, [k]: x }))
        )
    ), [{}]),
    getFlat = o => Object.entries(o).flatMap(([k, v]) => isObject(v)
        ? getFlat(v).map(([l, v]) => [`${k}.${l}`, v])
        : [[k, v]]
    ),
    input = { name: "Benny", department: { section: "Technical", branch: { timezone: "UTC" } }, company: [{ name: "SAP", customers: ["Ford-1", "Nestle-1"] }, { name: "SAP", customers: ["Ford-2", "Nestle-2"] }] },
    result = getCartesian(input).map(o => Object.fromEntries(getFlat(o)));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

This code locates all forks (places where arrays are located which indicate multiple possible versions of the input), and constructs a tree of permutations of the input for each fork. Finally, it runs all permutations through a flattener to get the desired dot-delimited result.

Note: h is a value holder, where h.s is set to 1 as soon as the first fork is found. This acts like a kind of global variable across all invocations of getFork on a particular initial object, and forces only one fork to be considered at a time when building up a tree of forks.

const input = {"name":"Benny","department":{"section":"Technical","branch":{"timezone":"UTC"}},"company":[{"name":"SAP","customers":["Ford-1","Nestle-1"]},{"name":"SAP","customers":["Ford-2","Nestle-2"]},{"name":"BAZ","customers":["Maserati","x"],"Somekey":["2","3"]}]}

const flatten = (o, prefix='') => Object.entries(o).flatMap(([k,v])=>v instanceof Object ? flatten(v, `${prefix}${k}.`) : [[`${prefix}${k}`,v]])
const findFork = o => Array.isArray(o) ? o.length : o instanceof Object && Object.values(o).map(findFork).find(i=>i)
const getFork = (o,i,h={s:0}) => o instanceof Object ? (Array.isArray(o) ? h.s ? o : (h.s=1) && o[i] : Object.fromEntries(Object.entries(o).map(([k,v])=>[k, getFork(v, i, h)]))) : o
const recurse = (o,n) => (n = findFork(o)) ? Array(n).fill(0).map((_,i)=>getFork(o, i)).flatMap(recurse) : o
const process = o => recurse(o).map(i=>Object.fromEntries(flatten(i)))

const result = process(input)
console.log(result)

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